A semiconductor memory device may improve its performance by controlling the refresh of weak cells having a short data retention time.
Semiconductor memory, such as dynamic random access memory (DRAM), may use a method of recording data by accumulating charge in a capacitor of a memory cell. The charge of the capacitor is lost in form of leakage current over time. To avoid data loss due to the leakage current, DRAM implements a refresh operation to read data from a cell and rewrite the read data in the cell before the data is lost completely.
The refresh operation may be carried out periodically or at the request of a system. Since capacitors of different cells may have different retention performances, e.g., different data retention times, a refresh operation taking into account such differences is desired.